The invention relates to improvements in positive displacement pumps, also known as volumetric pumps, and more particularly to improvements in pumps which operate or can operate at pressures of up to and above 2000 bar. Still more particularly, the invention relates to improvements in positive displacement pumps of the type wherein a fluid-admitting intake valve is coaxial with a fluid discharging outlet valve and wherein the two valves are coaxial with the fluid displacement body if the latter is a reciprocable body, such as a plunger.
A positive displacement pump of the above outlined character is disclosed, for example, in U.S. Pat. No. 5,147,189 granted Sep. 15, 1992 to Barnowski. The head of the pump housing is assembled of two parts and its height (as considered in the direction of the common axis of the intake and outlet valves) is considerable. The two-piece head has an internal compartment for nearly complete confinement of a composite insert which abuts the cylinder for the reciprocable plunger of the positive displacement pump. The insert extends across the plane of abutment between the two parts of the head as well as across the plane of abutment between the head and the casing of the pump. This can create problems when the pump is to deliver a highly pressurized fluid because such fluid is likely to leak between the two parts of the head and/or between the head and the casing of the pump housing, especially if the plane of contact between the two portions of the insert is located forwardly of and/or at a level above the plane of contact between the two parts of the head. The intake and outlet valves of the just described conventional pump are installed in the head of the pump housing, and this also creates problems when the pump is operated at an elevated pressure. Thus, the useful life of the composite pump head is shortened because the head is continuously subjected to stresses which fluctuate within a very wide range, namely between those which develop when the displacement body of the pump performs suction strokes and those which develop when the displacement body performs pressure strokes. Moreover, the just described pump is rather bulky and the cost of making and assembling its constituents, including the composite head and the composite housing, is high.